Modeling of CRACK PROPAGATION by finite element method under mixed mode conditions is of prime importance in fracture mechanics. This paper describes an application of finite element method to the analysis of mixed mode CRACK growth in linear elastic fracture mechanics. CRACK growth process is simulated by an incremental CRACK-extension analysis based on the maximum principal stress criterion, which is expressed in terms of the stress intensity factor.In this paper, a procedure to correct the direction of CRACK PROPAGATION in the analysis of finite element is presented to ensure that a unique final CRACK PATH is achieved for different analysis of a problem by using different increments of CRACK. For each increment of CRACK extension, finite element method is applied to perform a single region stress analysis of the CRACKed structure. Results of this incremental CRACK extension analysis are presented for several geometries.

Modeling of CRACK PROPAGATION by a finite element method under mixed mode conditions is of prime importance in the fracture mechanics. This article describes an application of finite element method to the analysis of mixed mode CRACK growth in linear elastic fracture mechanics. CRACK - growth process is simulated by an incremental CRACK-extension analysis based on the maximum principal stress criterion which is expressed in terms of the stress intensity factor. In this paper a procedure is employed to correct direction of CRACK PROPAGATION to ensure that a unique final CRACK PATH is achieved for different analysis of a problem by using different increments of CRACK. For each increment of CRACK extension, finite element method is applied to perform a single - region stress analysis of the CRACKed structure. Results of this incremental CRACK – extension analysis are presented for several geometries.

Use of CRACK PROPAGATION principles based on SIFs (stress intensity factors) is among the most common methods of fracture mechanic engineering. SIF is an important parameter in fracture analysis. In analyzing elastic fracture, SIF reveals the stress near the CRACK tip and substantial information about CRACK PROPAGATION. When loading or geometry of a structure is not symmetrical around a CRACK, rupture occurs with combined loading and the CRACK does not propagate on a straight line. Therefore, to determine the new direction of facture PROPAGATION use of twist angle criteria is necessary. The objective of this research was to propose a numerical model of CRACK PROPAGATION under combined loading conditions. In each CRACK with increased length the twist angle is assessed as a function of SIFs. This research aimed to determine SIFs for the CRACK PROPAGATION problem and to determine the CRACK development PATH through linear elastic fracture analysis. This study was primarily based on examination of the PROPAGATION and development of CRACKs on a plane under tensile loading and combined mode loading conditions. The ANSYS finite element software and FRANC3D CRACK PROPAGATION software were used to simulate CRACK PROPAGATION and to calculate the stress and SIFs.

In this paper, a two-dimensional computational model is proposed for predicting the initiation position and PROPAGATION PATH of subsurface CRACK of spur gear tooth flank. In order to simulate the contact of teeth, an equivalent model of two contacting cylinders is used. The problem is assumed to be under linear elastic fracture mechanic conditions and finite element method is used for numerical study. An initial subsurface CRACK is considered in the model at different depths. For each position of the initial CRACK, moving contact loading is applied to the part and value of DKII is obtained for the CRACK tips. The position of maximum DKII is selected as the location of CRACK initiation. It is shown that the subsurface CRACK appears at the maximum shear stress point. The maximum tangential stress criterion is used to determine the CRACK growth angle. The CRACK is incrementally propagated until the CRACK tip reaches the part surface and a cavity is formed on the tooth surface. Analyzing the stress field and stress intensity factors are performed in ABAQUS software. The obtained results for the depth and shape of the spall are in good agreement with the experimental results reported in literature.

In the present research, a fully Automatic CRACK PROPAGATION as one of the most complicated issues in fracture mechanics is studied whether there is an inclusion or no inclusion in the structures. In this study The Extended Finite Element Method (XFEM) is utilized because of several drawbacks in standard finite element method in CRACK PROPAGATION modeling. Estimated CRACK PATHs are obtained by using Level Set Method (LSM) in coupling with XFEM for 2D mixed mode CRACK PROPAGATION problems. Also, stress intensity factors for mixed mode CRACK problems are numerically calculated by using interaction integral method completely based on familiar PATH independent J-integral approach. However, the influence of the first non-singular term (T-stress) of Williams’ stress distribution series in a CRACKed body is considered. Different CRACK growth PATHs are calculated for different domains with predefined notches such as edge and center CRACKs. In addition, predefined CRACKs and inclusions are implicitly defined using enrichment procedure in the XFEM framework and the effects of soft or hard inclusions are studied on CRACK PROPAGATION schemes. Finally, estimated CRACK PATHs under assumed conditions by using XFEM, are compared with the experimental results.

The design, construction and installation of marine structures, according to the specific conditions of the implemented region and the loads on them, is in the field of the most advanced engineering issues, and today many researches have been carried out in its various fields under the loads caused by waves and sea currents. . One of the main issues in the design of marine platforms is the phenomenon of fatigue in connections., and fatigue analysis by different methods, including spectral and deterministic method and determining the fatigue life of the platform, is necessary. Due to the repetitive nature of the loads caused by the waves, the tubular members of the structure that are connected to each other with welded joints are exposed to repeated stresses and if the loading continues, rupture due to fatigue is likely. . Due to the special geometrical shape of these connections, there are points with high stress concentration, which are very prone to the phenomenon of fatigue, and for this reason, the fatigue analysis of structural connections as the weakest points against fatigue is one of the important factors in the design of platforms. In this research, the analysis of CRACK PROPAGATION due to fatigue in the connections of fixed offshore metal platforms has been discussed and the existing platforms in the Persian Gulf region have been used, which is the same as the SPD 15 platform located in the South Pars region. To prepare the model, the maps of the National Iranian Oil Company were used, and the wave force was applied to the structure in the main directions, and CRACK expansion analysis was performed. Abaqus software, which is a finite element program, has also been used for modeling.

The extent of economic damage due to brittle fracture may depend significantly on the PATH of CRACK growth. Therefore, it is important to develop appropriate techniques for predicting the PATH of CRACK growth in CRACKed components and structures. Although several methods are available for this purpose, the applications of these methods have been studied mainly for mode I CRACKs. The aim in this paper is to evaluate two available methods for predicting the PATH of brittle fracture for a given specimen subjected to pure mode II: "the method of incremental CRACK growth" and "the method of onset of fracture". The experimental PATH of fracture, already known from an earlier study, is used to investigate the accuracy of results obtained from the present methods. The maximum tangential stress criterion is employed to determine the fracture PATH in any of the above mentioned methods. The effect of a higher order term of stress on the PATH of CRACK growth is also studied. The computational results show that any of these two methods can provide an acceptable prediction for PATH of CRACK growth in the given specimen.    

The construction of Latiyan Buttress Dam was finished in 1968. The result of dam instrumentation indicated that till July of 1970 the dam was in a suitable situation. However at that time vertical CRACKs were observed on the walls of buttress 10/11, for the first time. These CRACKs were located on both sides of the gate control room, which extend from the crest level down to the floor of control room. The rehabilitation operations were done by injection of epoxy into the CRACK openings in winter 1970, but it did not work properly and the CRACKs opened again in summer 1971. Measurement of opening and closing of CRACKs shows a cyclic loop behavior affected by seasonal variations in temperature. The latter seems to be the major cause of CRACKing. In this study finite element analysis of CRACK PROPAGATION has been done by use of Nonlinear Fracture Mechanics concepts and Smeared CRACK Method. In this method its suggested that the CRACK will be replaced by a continuum with changeable physical properties. If the failure criterion is met, CRACKing takes place in the direction normal to the maximum principal stress. After CRACKing, the stiffness of concrete normal to the CRACK plane is reduced and concrete model becomes orthotropic. Therefore by PROPAGATION of CRACK in the structure the finite element mesh will not change while the material behavior relation changes. At first we find the distribution of temperature in the dam body by Heat Transfer Analysis for both summer and winter. Then by applying different static load combinations, the load combination that produce the CRACK is found. The result of static analysis demonstrates that applying the following load combination would cause high tensile stresses in the CRACKed region: Dam Weight + Hydrostatic Pressure + Summer Temperature Load + Lateral Pressure of Adjacent Blocks By analyzing of the model under cyclic temperature loads it is concluded that after a while the results should become steady and increasing the loading cycles does not make major differences in the results. We can conclude that by applying static loads the CRACK pattern wont propagate and the dam wont get in danger. It means that to keep services of this dam it is not necessary to do rehabilitation operations to resist static loads and the dam is safe in the normal loading conditions.

Recently, nitrogen alloyed steels have attracted the attention of researchers and industrial specialists due to their combination of strength and elongation. The identification of mechanical properties of nitrogen alloyed steels is very important for using these alloys with high reliability in various applications. Meanwhile, the resistance of material to CRACK PROPAGATION is one of the important parameters. Nowadays, nanoscience and computer simulations at nanoscale are noticed as the most studied subjects in the world. Molecular Dynamics Simulation (MDS) is one of the numerical methods at nanoscale which is the most deterministic method among available methods for the solution of molecular systems. The aim of this study is to simulate the CRACK PROPAGATION in Iron-Nitrogen nanocrystalline. In this regard, Iron-Nitrogen nanocrystalline is modeled by applying Modified Embedded Atom Method (MEAM) interatomic potential using the related parameters for Iron-Nitrogen alloy. The microstructure of CRACK growth in nanocrystalline with dimension 100A  40A  3A are investigated under tensile loading with velocity magnitude of 0. 8 Å /ps at temperature of 300K. The results show that CRACK velocity increases with the increase in CRACK length. The increase in the peak of radial distribution function curve during different time steps is as a result of change in the positions of particles during CRACK PROPAGATION. Also, the results indicates that the magnitudes of stress at three crystal directions has firstly nonlinear behavior and then changes to linear one which is due to the change of direction of CRACK growth during simulation time steps. Also, the track-growth direction and the track opening are investigated under simulation conditions.